Hammer mechanism



Oct. 13, 1964 Filed Sept. 18, 1961 Ha. I

F. G. PENSAVECCHIA ETAL 3,152,540

HAMMER MECHANISM 3 Sheets-Sheet 1 IN V EN TORI Q mm .pzwsn VICFRAN/AJUGGAI R. 8

05: 1; fife M A TTO/P/VEY 1964 F. G. PENSAVECCHIA ETAL 3,152,540

HAMMER MECHANISM Filed Sept. 18, 1961 s SheetsSheet 2 A 7' TOR/V5 Y Oct.13, 1964 F. e. PENSAVECCHIA ET AL 3,152,540

HAMMER MECHANISM 3 Sheets-Sheet .5

Filed Sept. 18, 1961 IN VEN TORS FRANK 6. PEA/SA VECLfl/A HUG/1' R.BAR/V55 ATTORNEY United States Patent 3,152,540 HAMMER MECHANISM FrankG. Pensavecchia, Orchard Lake, and Hugh R. Barnes, St. Clair Shores,Mich, assignors, by mesne assignments, to Holley Computer ProductsCompany, Warren, Mich, a corporation of Michigan Filed Sept. 18, 1361,Ser. No. 138,910 8 Claims. (Cl. 101-93) This invention relates to anelectro-mechincal printer, and particularly to a novel on-the-fly typeprinter.

More specifically, this invention relates to an improvement in theprinter hammer mechanism disclosed in US. application Serial No. 138,157entited High Speed Printer and filed on September 14, 1961 in the namesof Arvin D. McGregor and James M. Irvine, Jr.

The printer disclosed in the above referenced application Serial No.138,157, hereinafter referred to as the prior construction, contains arow of print hammers 160 guided for reciprocating movement toward andaway from the print drum 169, each hammer having associated therewith aninterposer system including an actuating lever 215 and a so-calledbeaver tail 182 which is positioned so as to be struck by a lobe 241 ofthe continuously rotating cam 108 when the actuating lever is notretained in the non-print position by an electromagnet 226.

The prior construction, including its operation and control, iscompletely described in the above mentioned application Serial No.138,157, the disclosure of which is incorporated herein by reference toany extent that it may be necessary to complete this disclosure. Thus,except for occasional reference thereto, the above prior constructionwill not be described further in any great detail except to say that itinvolved a number of moving parts for each hammer and a bail bar 243,the bail bar being provided to prevent a possible meaningless line ofprint when the printer was first turned on.

It is now proposed to provide a print hammer mechanism in which there isbut one moving part in addition to the print hammer itself and the printcam.

Another object of the invention is to provide a mechanical amplifiertype of print hammer mechanism in which a print cam is employed, butwhich does not include a lever type interpcser system so that the printcam strikes the print hammer directly.

Another object of the invention is to provide a print hammer mechanismin which the print hammer is retained in the non-print position awayfrom the cam by means of a spring-loaded solenoid plunger engaging ashoulder on the print hammer, the print hammer being spring urged to theprint position upon energizing the solenoid associated with the printhammer.

Another object of the invention is to provide a hammer mechanism inwhich a rotating cam impacts a freeflight, projectile type hammer whenit is moved by spring means from a non-print position outside the outerdiameter of the cam to a print position within the outer diameter of thecam, but wherein the non-print position of the hammer is a sufiicientdistance outside the outer diameter of the cam so that the hammer has arunning start and thus a greater velocity during its movement from theouter diameter to the print position.

Another object of the invention is to provide a print hammer mechanismin which all hammers addressed for printing at the same time areuniformly positioned against a single stop member.

A further object of the invention is to provide a hammer bank assemblythat may be substituted for the hammer bank assembly shown in FIGURE 7of the above referenced application Serial No. 138,157. w

Another object of the invention is to provide a hammer bank assemblythat is easier to construct and repair than the hammer bank assemblyshown in FIGURE 7 of the above referenced application Serial No.138,157.

A still further object of the invention is to provide a print hammermechanism that is simpler in operation, less expensive to construct,less likely to require service and easier to repair than the hammermechanism disclosed in application Serial No. 138,157.

These and other objects and advantages of the invention will become moreapparent upon reference to the following specification and the attacheddrawings wherein:

FIGURE 1 is an elevational view, with portions thereof cut away, of aprint hammer bank assembly embodying the invention.

FIGURE 2 is a fragmentary end elevational View of the hammer assemblyshown in FIGURE 1, when viewed from the right-hand end of FIGURE 1.

FIGURE 3 is an end elevational view looking at the left end of FIGURE 1.

FIGURE 4 is a fragmentary top plan view of the left portion of theassembly shown in FIGURE 1.

FIGURE 5 is an enlarged, fragmentary cross-sectional view taken on theplane of line 55 of FIGURE 1 and looking in the direction of the arrows.

Referring to the drawings in greater detail, a hammer bank assembly 10embodying the invention comprises a main casting or support member 12having a base portion 14 and spaced end portions 16. As in the priorconstruction, the base portion is provided with slots 18 so as to enableadjustment of the main support 12 in securing the same to the main frameof the printer.

A multiple lobe print cam 20 is mounted between the end portions 16,with the cam shaft ends 22 and 24 being mounted in suitable bearings andsecured by means of the cap members 26. The cam lobes 28 are preferablyformed with circle involute profiles 30, and the cam is driven at aconstant predtermined speed, in the same manner and for the same purposeas in the prior construction.

A cam drive pulley 32 is mounted on the shaft end 22, and a timing wheel34 is mounted on the opposite shaft end 24 so as to be rotatable withthe cam. The timing wheel 34 is provided with circumferentially spacedferro-magnetic segments 36 for cooperation with the magnetic pickup 38so as to signal the position of the lobes 23 of the cam, all in the samemanner as explained in the prior construction.

Upper and lower print hammer guide members 40 and 42, respectively, aremounted on the end portions 16 so as to extend therebetween. The spacingbetween members 41) and 42 is determined by the end members 41, whichare secured by the same bolts 43 that secure the upper guide 49. Likethe prior construction, the upper and lower guide members 40 and 42 areprovided with vertically aligned slots 44, each pair of verticallyaligned slots having a plate 46 inserted therein so as to provide aseries of adjacent spaces 48 in which the individual print hammers 50are positioned and through which the print hammers are actuated towardand away from the print drum Hi9. It will be noted that the plates 46are retained in one direction by a tab 45 thereon engaging the upperguide member 40 and in the opposite direction by the hammer 62 engagingthe edges thereof. Removal of member 62 permits easy removal of anyplate 46, hammer 50 or hammer spring 60. A spring guide pin 61 for eachspring 60 is formed or mounted on the member 62 in order to facilitateassembly and disassembly of hammer bank.

The print hammers 50, the number of which corresponds to the number ofcharacters in the rows of characters formed on the drum 109 areidentical to each other in construction. Essentially, these printhammers comprise a generally rectangular body preferably formed from amaterial that is strong, light in weight, resilient and self-lubricatingand that has a known and suitable fatigue limit. Delrin is such amaterial, and the hammers are preferably injection molded from thismaterial in a single cavity mold so as to assure that the hammers aresubstantially identical in configuration and Weight. The hammers arepreferably formed with openings 51 and/ or reductions in cross-sectionto further reduce the weight thereof, and each hammer has formed on orsecured thereto at one end thereof a relatively hard characterimpactingsurface or member 52.

The adjacent surfaces of the upper and lower guide members are parallel,and they are positioned such that the lines of action of the printhammers guided thereby pass through the axis of the print drum. Theopposite end of each print hammer is formed with a fiat surface 54 thatis preferably normal to the above line of action of the print hammer.

Each print hammer is formed near the character impacting end thereofwith a cut out portion 56 providing an abutment 58 for one end of thespring 6f), the other end of the spring being seated against theretainer bar 62 that extends along the entire length of the lower guidemember 42 and that is secured thereto by any means such as the screws64. In other Words, each of the print hammers 50 positioned in a space48 has associated therewith a spring 69 compressed between the shoulder58 on the print hammer and the elongated spring retainer 62. This springof normally urges the print hammer 58 away from the print drum SW9 andtoward the print cam until the fiat surface 54 of the print hammer is inengagement with the elongated stop member 66 secured in any manner, suchas by means of the screws 68, to the upper guide member 40. Thus, withonly the structure explained thus far, all print hammers 50 in the printhammer bank It would be urged by their respective springs 69 to thedotted line position, as shown in FIGURE 5, against the common stopmember.

In this dotted line position, the print hammers 50 are in the path oftravel of the cam lobes 28, and any print hammer 59 so positioned wouldbe impacted with a constant velocity along the line of action of theprint hammer against the force of the return spring 60. The constantvelocity and direction is assured by the involute profile of the camlobes 28 striking the flat surfaces 54 which are normal to the lines ofaction of the print hammers, as explained in connection with FIGURE 16of the above referenced application Serial No. 138,157.

The print drum 109 has axial rows of identical characters formedthereon, the characters of each row usually being different from thosein another row, and there are the same number of print hammers in thebank 10 as there are characters in a row of characters formed on thedrum 109. However, it is desired to print only certain preselectedcharacters from any row of characters on any line of print, dependingupon information and signals supplied by the computer with which theprinter is employed.

The immediate means for addressing the individual print hammers 50thatis, placing any given print hammer 50 in the dotted line printposition-comprises a solenoid 70 associated with each print hammer.These solenoids may be ordinary solenoids having a movable core orplunger 72 urged away from the solenoid body by a spring when thesolenoid coil is not energized and drawn into the solenoid body When thesolenoid coil is energized.

Each print hammer 50 is formed along one edge thereof with a cut outportion or slot 74 adapted to receive the extended plunger 72 of itsassociated solenoid when the solenoid 70 is in the unenergized state. Aninsert 76 secured at the end of the slot 74 provides an abutment toengage the extended plunger 72 and retain the hammers 50 in thenon-print position shown in solid lines in FlGURE 5 against the force ofthe return spring 60 tending to move the hammer to the dotted line printposition. A hammer will remain in this non-print position until asuitable signal (equivalent to the pulse coil energizing signal of theprior construction) results in the solenoid being energized to withdrawthe plunger 72 from the slot 74 and permit the return spring 60 to movethe hammer rearwardly against the stop 66.

While it is not necessary to the operation of the hammer, the upper edgeof the hammer is formed with camming ramps 71 and 73 to enable insertionand removal of the hammer without removing or energizing its solenoid70.

It is apparent that the spacing of the hammers 50 is determined by thespacing of the characters in the row of characters formed on the printdrum and that there must be a separate solenoid for each print hammer.Inasmuch as the diameter of the solenoids is greater than the width of aprint hammer, the solenoids are preferably mounted in slanted groups, asbest seen in FIGURE 4.

Each solenoid 70 comprises a main body with a reduced cylindrical orother end portion 78, the movable plunger 72 being biased outwardly bythe usual spring provided inside each solenoid body.

The upper guide member 40 may be formed with a recess 30 extending alongthe entire bank of hammers and being sufficiently wide to receive agroup of solenoids 79, four solenoids being shown in this particularembodiment. The bottom Wall of the recess 8-9 is formed with similarlygrouped annular passages 84, the axis of each passage passing throughthe central plane of its associated hammer 50. Each solenoid 70 is thenplaced in the recess 86 so that the reduced portion 78 thereof fits intoone of the passages 84, and a holding bracket 86 is secured to the upperguide member 40 in a manner to hold one group of the solenoids 70. Inthis case, four solenoids 7tl are held by a single bracket 86, which mayhave openings 88 to receive the solenoid leads 90; it is apparent,however, that some other solenoid grouping and that some other securingmeans could be employed.

Operation The hammer bank 1-0 would be secured on the main frame of theprior printer with the character impacting ends 52 of the row of hammersbeing positioned adjacent the print drum, as shown in FIGURE 3 and inthe manner of the prior construction.

In general, the print drum and the cam may be the same or similar tothose of the prior construction, and they would be driven in the samemanner as shown in FIGURE 5 of the above referenced application. Thetiming wheel and the magnetic pickup associated therewith may also bethe same in construction, operation and purpose as in the priorconstruction. The energization of the individual hammer solenoids 70would be accomplished in essentially the same manner as the energizationof the pulse coils of the prior construction, any differences inmagnitude and duration of pulses being a matter of design.

It is thus apparent that the improved hammer mechanism described hereindoes not require either the holding coils and associated circuitry orthe bail bar of the prior construction.

Except when actually printing, the print hammers 50 are retained in thesolid line non-print position of FIG- URE 5 by the spring-biasedsolenoid plunger 72 engaging the shoulder 76 on the print hammer.Energization of any given hammer solenoid 70 for printing may be of suchshort duration that the plunger 72 is already extended by its springbefore the hammer 50 has been impacted by the cam 20; in that event, theagain extended plunger 72 will ride along the top edge of the hammer 50during its final travel to the stop 66 and immediately after impactuntil the abutment 76 passes the plunger 72,

at which time the plunger will extend itself further into the slot, justas it is in the non-print condition. Thus, the plunger 72 will be in theslot 74, which is sufficiently long so as not to interfere with thetravel of the hammers St! on impact, even before the impacted hammerreaches the print drum. In other words, the plunger 72 is alreadywaiting for the shoulder 76 to engage it and maintain the hammer St inthe solid line non-print position until the next time that particularsolenoid is energized.

Assuming that the printer has been in operation for some given time, thevery last signal received from the computer to print certain charactersand complete a line of print will necessarily and automatically resultin the hammers involved being impacted and returned to the non-printposition immediately thereafter. Since the operator does not normallyshut off the printer until after a printing job has been completed, allof the hammers of the printer will already be in the non-print positionwhen the printer is shut down.

It is thus apparent that the construction of this invention eliminatesthe need for the bail bar, the interposer lever system, and the hammerelectromagnets of the prior construction disclosed in application SerialNo. 138,157. Since all of the print hammers are in their non-printposition on shut down of the printer and remain in that condition untilthe printer is again turned on and a new print signal is given toenergize one or more of the hammer solenoids 7t), there is nopossibility of a meaningless line of print when the printer is turned onbecause the cam lobes cannot strike a hammer even though the cam isrotating.

No printing can occur until a proper signal is received from thecomputer to energize one or more of the hammer solenoids 7d, at whichtime the solenoid plunger 72 is drawn into the solenoid body and awayfrom the shoulder 76 of the print hammers Si? and the return spring 60moves the hammer away from the print drum and against the stop 66. Allprint hammers thus addressed for printing from a single row ofcharacters on the print drum will be struck simultaneously by theinvolute profile surface of one of the cam lobes 23. Regardless of anypossible variation of the print hammers along their lines of action duepossibly to variations in the surface of the stop member 66, theinvolute profile cam lobe 28 will strike all addressed print hammerstoward the print drum with a constant velocity and direction, asexplained in connection with the prior construction. These impactedhammers will be returned by the force of the return spring and stop in anon-print position due to the reextended solenoid plunger 72.

Before the next succeeding cam lobe reaches the dotted line position ofFIGURE 5, all hammers required to print from the next succeeding row ofcharacters formed on the print drum will have been addressed byenergization of their respective solenoids and reached the dotted lineposition of FIGURE 5 against the stop on, waiting to be impacted by thenext succeeding cam lobe.

It is important in the operation of the hammer mechanism of thisinvention, and in the design of the printer generally, that the frictionof the hammer 50 against the solenoid plunger 72 be maintained at aminimum. This, of course, enables the use of a physically smaller andlower power solenoid. It is also important that the hammer move from theouter diameter AB of the cam 20 to its dotted line print position asfast as possible so as to require less rotation of the cam than wouldotherwise be necessary for this same hammer motion and thus provide agreater safety factor in the operation of the mechanism in view ofvariables such as hammer friction, hammer spring rate and pre-load andsolenoid actuation time.

It is obvious that the corner 92 of the hammer, when it is in the solidline non-print position, must be outside the outer diameter AB of thecam lobes in order that the lobes of the rotating cam will not strikethe hammer. This could be accomplished by positioning the corner 92 ofthe hammer very close to this outer diameter so that the lobes just missthe hammer. However, it has been found that the operation of themechanism is greatly im proved, all other things being equal, if thecorner 92 of the hammer is stopped some greater distance away from theouter diameter. This greater clearance, in effect, gives the hammer arunning start so that its velocity from the time it reaches the outerdiameter AB of the cam to the time that it reaches the stop 66 isgreater than it would be if its initial stopped position were very closeto the outer diameter of the cam. This permits the use of a lower ratespring and/or a lower pre-load of the spring, thus reducing the sidethrust or friction of the hammer against the solenoid plunger. Reducingthis friction reduces the power required to be supplied to the solenoid.The greater clearance permits the hammer to reach a stable stoppedposition sooner, which results in a better impact of the hammer by thecam.

As explained in application Serial No. 138,157 referred to above, a codedisk assembly secured for rotation with the print drum signals what rowof characters on the drum is approaching the print station so that thosecharacters could be printed. The timing wheel and magnetic pickupprovide a signal to indicate when a cam lobe is approaching a positionto impact addressed hammers. These signals are processed by thecomputerprinter electronics and finally result in a signal to theprinter telling it which hammer solenoids must be energized so thattheir associated hammers may print by impact from the next cam lobe.

It is apparent from the above description that a simpler operating andless expensive hammer mechanism has been provided by the use of theinvention. This hammer mechanism is easily assembled in a hammer bankassembly that can be substituted for the hammer bank assembly of theprior construction. The same type of signals that energized the pulsecoils of the prior construction could be used to energize the solenoids7th of the present construction. Any changes in the circuitry of theprior construction necessitated by the substitution therein of a hammerbank assembly embodying this invention are minor and deemed to be amatter of ordinary skill. For example, no holding coil circuitry isrequired; also as stated above, the prior bail bar construction may beentirely eliminated.

While but one embodiment of the invention has been shown and described,it is apparent that modifications can be made within the scope of theappended claims.

What We claim as our invention is:

1. In a printer having a continuously rotated drum with rows ofcharacters formed thereon, a row of print hammers positioned adjacentsaid print drum, a single continuously rotated impact means positionedon the side of said row of print hammers opposite said print drum, eachof said print hammers comprising a body mounted for reciprocatingmovement toward and away from said print drum upon being struck by saidimpact means, the line of action of each of said hammers passing throughthe center of said print drum, a compression spring positioned between afixed abutment and a shoulder formed on each of said hammers, saidspring urging said print hammer away from said print drum and into thepath of said impact means, a fixed stop member limiting the movement ofeach of said hammers away from said print drum by said spring anddefining a common position for striking said hammers by said impactmeans, means for retaining each of said hammers in an intermediateposition away from said fixed stop but with its extreme end out of thepath of said impact means, said means comprising an abutment formed onone edge of each of said hammers and a solenoid-operated latch engagedby said abutment.

2. A hammer bank assembly for a high speed printer having a print drumwith axial rows of identical characters formed thereon, said assemblycomprising a main support member having spaced end supports, anelongated multiple lobe cam mounted on said end supports so as to berotatable therein, means for driving said cam, means for signaling theposition of the lobes of said cam during the rotation thereof, upper andlower guide members mounted on said side supports in parallel spacedrelation, said guide members having vertically aligned slots formedtherein, a spacer plate positioned in each pair of vertically alignedslots so as to provide the same number of guide spaces as there arecharacters in a row of characters formed on the drum, a print hammerpositioned in each of said guide spaces, a single elongated hammer stopmember secured to the end of said upper guide member adjacent said earn,an elongated abutment member secured to the end of said lower guidemember adjacent said print drum, a compression spring positioned in eachof said guide spaces between said abutment member and a shoulder formedon the print hammer positioned therein, said spring urging said hammerinto the path of said cam and toward said stop, means associated witheach of said print hammers for preventing said print hammers from beingimpacted by said cam, said means comprising an abutment formed on theupper edge of said print hammer and a movable latch, said latch beingurged into engagement with said abutment by a spring and drawn out ofengagement with said abutment by a solenoid, said solenoids beingpositioned and secured in said upper guide member.

3. In a printer having a rotatable print drum and a print hammer impactmeans, a print hammer system mounted intermediate said drum and saidimpact means, said impact means at times projecting said print hammersystem toward said print drum, said system comprising a slidably mountedprint hammer, a fixed stop at each end of said print hammer, one of saidstops limiting the movement of said hammer toward said impact means, acut out portion near each end of said hammer, a compression spring insaid cut out portion at the drum end of said hammer and retained thereinby one of said fixed stops, said spring returning said hammer to saidone of said stops, a solenoid fixedly mounted adjacent to and within thelongitudinal limits of said hammer, and a moveable latch at timesextending from said solenoid into said out out portion at the other endof said hammer.

4. In a printer having a rotating print drum, a projectile type printhammer, first means for at times impacting said print hammer, secondmeans for urging said print hammer into the path of said first means,third means for at times contacting and thereby preventing said secondmeans from positioning said hammer in the path of said first means, andsloped camming ramps formed on said print hammer between said thirdmeans and the impact end of said print hammer for permitting insertionand removal of said print hammer without removing or energizing saidthird means, said third means riding on a surface on said print hammerand being alternately lifted and lowered by said camming ramps duringthe insertion and removal of said print hammer.

5. In a printer having a rotating print drum, a projectile type printhammer, a rotating element for at times impacting said print hammer,spring means for urging said print hammer into the path of said element,solenoid means having a spring-biased latch extending therefrom into aslot formed on said hammer for preventing said first means frompositioning said hammer in the path of said element, and sloped two-waycamming ramps formed on the impact end of said print hammer for duringthe insertion and removal by said print hammer. without removing orenergizing said solenoid means, said latch riding on a surface on saidprint hammer and being alternately lifted and lowered by said cammingramps during the insertion and removal of said print hammer.

6. A printer, comprising a print drum, a support member, a row of printhammers mounted in said support member and an elongated rotatable camfor impacting said print hammers toward said drum, each of said hammerscomprising a body having length, width and thickness and beingreciprocable through a slot formed in a support member, each of saidhammers being urged toward said cam by a compression coil springpositioned in a slot formed in the print drum end of said hammer andconfined Within said slot through which said hammer reciprocates, oneedge of each of said print hammers having a slot adapted to receive aspring-loaded and solenoid-operated latch so as to prevent said firstspring from positioning said print hammer in the path of said cam exceptwhen said solenoid is energized, the upper edge of each of said printhammers between said latch-receiving slot and the cam end thereof havingfront and rear cam surfaces enabling the insertion and removal of saidprint hammer through said slot from the drum end of said support memberwithout removing said latch or energizing said solenoid, said latchriding on a surface on said print hammer and being alternately liftedand lowered by said cam surfaces during the insertion and removal ofsaid print hammer.

7. In a printer having a base member, a rotatable print drum, an impactmeans, a print hammer, means on said base for guiding said hammer, saidhammer having a longitudinally extending recess at that end of thehammer nearest said drum, said recess being formed with an abutmentspaced from said end, a compression spring mounted in said recess, thewidth of said spring being substantially equal to the width of saidhammer, spring retaining means on said base, said spring being confinedby said retaining means and said abutment and urging said hammer towardsaid impact means, said hammer having a second abutment, a latchpositioned between said drum and said impact means normally engagingsaid second abutment to hold said hammer away from said impact meansagainst the force of said spring, and solenoid means for withdrawingsaid latch from engagement with said hammer.

8. In a printer as defined in claim 7, said second abutment beingdisposed between the ends of said hammer.

References Cited in the file of this patent UNITED STATES PATENTS2,766,686 Fomenko et al Oct. 16, 1956 2,792,779 Toeppen et a1. May 21,1957 2,895,411 Demer et al July 21, 1959 2,897,752 Malmros et al Aug. 4,1959 2,949,846 Hoffman et a1. Aug. 23, 1960 2,997,632 Shepard Aug. 22,1961

7. IN A PRINTER HAVING A BASE MEMBER, A ROTATABLE PRINT DRUM, AN IMPACTMEANS, A PRINT HAMMER, MEANS ON SAID BASE FOR GUIDING SAID HAMMER, SAIDHAMMER HAVING A LONGITUDINALLY EXTENDING RECESS AT THAT END OF THEHAMMER NEAREST SAID DRUM, SAID RECESS BEING FORMED WITH AN ABUTMENTSPACED FROM SAID END, A COMPRESSION SPRING MOUNTED IN SAID RECESS, THEWIDTH OF SAID SPRING BEING SUBSTANTIALLY EQUAL TO THE WIDTH OF SAIDHAMMER, SPRING RETAINING MEANS ON SAID BASE, SAID SPRING BEING CONFINEDBY SAID RETAINING MEANS AND SAID ABUTMENT AND URGING SAID HAMMER TOWARDSAID IMPACT MEANS, SAID HAMMER HAVING A SECOND ABUTMENT, A LATCHPOSITIONED BETWEEN SAID DRUM AND SAID IMPACT MEANS NORMALLY ENGAGINGSAID SECOND ABUTMENT TO HOLD SAID HAMMER AWAY FROM SAID IMPACT MEANSAGAINST THE FORCE OF SAID SPRING, AND SOLENOID MEANS FOR WITHDRAWINGSAID LATCH FROM ENGAGEMENT WITH SAID HAMMER.